Try and get fit on a bike by someone who knows what they are doing. But in the end it comes down to what is comfortable. My wife is about 5'10" so when we bought her bike we skipped right past the women's bikes and looked at the men's. Our LBS will help fit your bike, actually spent quite a bit of time with her to get it right. She ended up with a slightly smaller bike than I imagined, a 54cm road bike even though she would fit just fine on a 56cm, but she felt a little more relaxed and comfortable on the smaller frame so that's what we bought. Basically, just try them all out and see what fits best.